Remove `Type` parameter from SymbolTable::insert(). NFC.

`Type` parameter was used only to check for TLS attribute mismatch,
but we can do that when we actually replace symbols, so we don't need
to type as an argument. This change should simplify the interface of
the symbol table a bit.

llvm-svn: 344394
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index 7a35377..0ed0ef6 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -110,6 +110,8 @@
   case Symbol::LazyObjectKind:
     assert(Sym.IsUsedInRegularObj && "lazy symbol reached writer");
     return 0;
+  case Symbol::PlaceholderKind:
+    llvm_unreachable("placeholder symbol reached writer");
   }
   llvm_unreachable("invalid symbol kind");
 }